Deck 3: Thermodynamics of Biological Systems

Question 1

Given the following reaction, what can be said about the equilibrium concentrations of the components of the reaction? (do not assume that concentrations began at standard conditions)
Pyruvate + NADH + H⁺
Lactate + NAD⁺
ΔG°′ = −25.2 kJ/mol

A) [pyruvate] > [NADH]
B) [pyruvate] < [NAD⁺]
C) [NAD⁺] > [NADH]
D) [pyruvate] > [lactate]
E) cannot determine

Answer 1

E

Question 2

Which example has the greatest increase in entropy, ΔS?

A) freezing water
B) sublimation of CO₂
C) melting ice
D) shattering glass
E) boiling gasoline

Answer 2

B

Question 3

An interaction between two subunits of a protein was determined to have a ΔG°′ = −57.05 kJ/mol. What is the K_eq for the reaction at 25°C?

A) 1.02
B) 1.32
C) 10−¹⁰
D) 10¹⁰
E) cannot determine from given information

Answer 3

D

Question 4

Entropy, S, is exactly zero at:

A) 25°C
B) 0°C
C) 25°K
D) 0°K
E) 38°C

Question 5

Thermodynamics does NOT:

A) describe the flow and interchange of heat, energy, and matter.
B) allow the determination of whether a reaction is spontaneous.
C) provide information on the rate of a reaction.
D) consider heat flow and entropy production.
E) consider the effect of concentration on net free energy change of a reaction.

Question 6

An example of an open system would be:

A) a chemical reaction taking place in a closed beaker.
B) a steam radiator.
C) an insulated bomb reactor.
D) a pot of boiling water.
E) contents of a calorimeter.

Question 7

Virtually all life on earth depends on energy ULTIMATELY from:

A) the power company.
B) batteries.
C) the green-house effect.
D) the sun.
E) activation energy.

Question 8

Thermodynamic parameters (entropy, enthalpy, free energy, and internal energy) are given for an unknown enzyme. Explain which results would be expected for the breaking of hydrogen bonds and the exposure of hydrophobic groups from the interior during the unfolding process of a protein.

A) Entropy change, ΔS, is zero
B) Enthalpy change, ΔH, is positive
C) The reaction is spontaneous
D) Enthalpy change, ΔH, is negative
E) Entropy change, ΔS, is positive

Question 9

"High-energy" compounds exhibit large negative free energy of hydrolysis and include all EXCEPT:

A) phosphate esters.
B) enol phosphates.
C) acyl phosphates.
D) guanidino phosphates.
E) thioesters.

Question 10

Which equation defines a system at equilibrium?

A) ΔG > 0
B) ΔG° = ΔG
C) ΔG = 0
D) ΔG° = 0
E) ΔG = RT ln ([products]/[reactants])

Question 11

Enthalpy change, ΔH, is:

A) the sum of heat absorbed and work.
B) not a thermodynamic state function.
C) a measure of disorder in a system.
D) determined by pressure change at a constant temperature.
E) equal to the heat transferred at constant pressure and volume.

Question 12

Which of the following statements is true for the Second Law of Thermodynamics?

A) Systems tend to proceed from disordered states to ordered states.
B) The entropy of the system plus its surroundings is unchanged by reversible processes
C) The entropy of the system plus its surroundings decreases for irreversible processes.
D) Naturally occurring processes never proceed toward equilibrium.
E) All of the above are true

Question 13

To predict whether pairs of coupled reactions will proceed spontaneously:

A) Subtract the smaller from the larger ΔG.
B) Sum the ΔG°′ values for each reaction.
C) Add the ΔS values for each reaction at constant temperature.
D) The absolute value of the positive ΔG°′ must be larger than the value of the negative ΔG°′.
E) None are true.

Question 14

Which statement pertaining to the three basic systems is true?

A) The internal energy of an isolated system is mostly conserved.
B) Open systems can exchange matter with other open systems.
C) Open systems can exchange matter with a closed system.
D) The internal energy of an open system is always constant.
E) A closed system can accept heat from an isolated system.

Question 15

All are true about ΔG EXCEPT?

A) A positive or negative ΔG tells us which direction the reaction will proceed.
B) ΔG depends upon the concentration of the reactants and products.
C) ΔG is affected by temperature.
D) ΔG is affected by pressure and pH.
E) ΔG is negative for endergonic reactions.

Question 16

Entropy change, ΔS, is

A) the sum of heat absorbed and work.
B) not a thermodynamic state function.
C) a measure of disorder in a system.
D) determined by pressure change at a constant temperature.
E) equal to the heat transferred at constant pressure and volume.

Question 17

Living systems are:

A) closed systems exchanging only energy with the surroundings.
B) isolated systems that are totally contained.
C) open systems exchanging only energy with the surroundings.
D) open systems exchanging both energy and matter with their surroundings.
E) none of the above.

Question 18

Based upon the following reactions, what would be the ΔG°′ for the formation of ATP from phosphoenolpyruvate and ADP?
ATP → ADP + Pi
ΔG°′ = −31.5 kJ/mol
Phosphoenolpyruvate → pyruvate + Pi
ΔG°′ = −62.2 kJ/mol

A) −93.7 kJ/mol
B) −30.7 kJ/mol
C) +30.7 kJ/mol
D) +93.7 kJ/mol
E) cannot determine from given information

Question 19

All describe modified standard state for a thermodynamic parameter EXCEPT:

A) designated with a prime ( ′ ) symbol.
B) H⁺ ion of 10^-7 M.
C) 10^-6 M for solutions.
D) 1 atm. for gases.
E) When the solvent is water at pH = 7.

Question 20

The standard state free energy change, ΔG, is:

A) positive when the reaction is unfavorable.
B) an expression of K_eq.
C) negative when the reaction is favorable.
D) equal to ΔH − TΔS.
E) none of the above.

Question 21

​Discuss the relationship between the Gibbs free energy (G°') of adenosine triphosphate (ATP) hydrolysis and Mg²⁺ concentration, and how this relationship is affected by pH.

Question 22

The reduction of pyruvate to lactate has an E_o′ of -0.185 V while the reduction of acetaldehyde to ethanol has an E_o′ of -0.197 V. If these two reactions are coupled to produce a spontaneous reaction, which of the following would be the reducing agent?

A) pyruvate
B) lactate
C) acetaldehyde
D) ethanol
E) cannot be determined from the given information

Question 23

The chemical reasons for the large negative ΔG°′ for the hydrolysis of ____ include destabilization of the reactant due to bond strain caused by electrostatic repulsion, stabilization of the products by ionization and resonance, and entropy factors due to hydrolysis and subsequent ionization.

A) AMP
B) ATP
C) PEP
D) Phosphocreatine
E) All of the above

Question 24

The hydrolysis of a phosphate from which of the following molecules is most thermodynamically favorable?

A) ADP
B) glucose phosphate
C) adenosine-5'-diphosphate
D) phosphoenolpyruvate
E) adenosine-5'-triphosphate

Question 25

____ and ____ are a small family of universal biomolecules mediating the flow of energy from exergonic reactions to the energy requiring processes of life.

A) Reduced coenzymes, caffeine
B) High-energy phosphate compounds, caffeine
C) Chlorophyll, caffeine
D) Hemoglobin, chlorophyll
E) Reduced coenzymes, high-energy phosphate compounds

Question 26

Which of the following statements about ATP is NOT true?

A) It is used for short-term energy in the cell.
B) It has two phosphoanhydride bonds.
C) The reason for the large −ΔG° values of hydrolysis reactions is due to stabilization of products.
D) ATP is usually complexed with Mn²⁺.
E) ATP is a kinetically stable molecule.

Question 27

What information do thermodynamic parameters provide about biochemical events?​

Question 28

For the reaction of ATP + H₂O -> ADP +Pi + H⁺, the biochemical standard state conditions would include all of the following EXCEPT:

A) the concentration of ATP would be 1 M
B) the temperature would be 25°C
C) the concentration of protons would be 10^-7 M
D) the concentration of water would be 1 M
E) all to the above are correct

Question 29

ATP hydrolysis coupled reactions have equilibrium constants that are changed by a factor of:

A) 10
B) 100
C) 10⁴
D) 10⁶
E) 10⁸

Question 30

Which statement MOST COMPLETELY EXPLAINS the large ΔG° for the hydrolysis of phosphoenolpyruvate?

A) Hydrolysis of the phosphate bond along with the conversion of the enol to the keto form of pyruvate.
B) The hydrolysis of the phosphoanhydride bond.
C) Conversion from the enol to the keto form of pyruvate.
D) Strong bond energy along with a change in the stereochemistry of the molecule.
E) The large ΔG° of the phosphoester bond.

Question 31

The metabolite with a lower ΔG°′ of hydrolysis than ATP is:

A) acetyl phosphate.
B) phosphoenol pyruvate (PEP).
C) phosphocreatine.
D) adenosine-5'-phosphate.
E) pyrophosphate.

Question 32

The effects of ____ on the ΔG°′ of hydrolysis of ATP are much greater than the effects of ____ or ____ under physiological conditions.

A) pH, concentration, metal ions
B) metal ions, pH, concentration
C) temperature, concentration, pH
D) concentration, pH, metal ions
E) none of the above.

Question 33

Which of the following statements regarding ATP is true?

A) the energy of hydrolysis is the same for all of the phosphate groups of the molecule
B) despite the very exergonic nature of the hydrolysis, ATP does not hydrolyze spontaneously due to a very high activation energy
C) the ΔG of hydrolysis within the cell is substantially greater than the ΔG°′ due to a higher concentration of ATP with respect to ADP
D) electrostatic attraction of the phosphate groups contributes to a more exergonic free energy
E) both b and c are correct

Question 34

Biochemists define the group transfer potential as the ____ that occurs upon hydrolysis (i.e., transfer of the particular group to water).

A) ΔG
B) ΔH
C) ΔS
D) ΔC_p
E) ΔE

Question 35

Define the three state functions that describe the energetics of biochemical reactions. Write the relationship between the three state functions.​

Question 36

Explain in brief the significance of adenosine triphosphate (ATP) as an intermediate energy-shuttle molecule.​

Question 37

A widely used "consensus value" for ΔG°′ of ATP hydrolysis in biological systems is ____ kJ/mol.

A) −21
B) −30.5
C) −7
D) 3
E) 21

Question 38

The association of a protein and a fragment of DNA has a ΔG°′ of -57 kJ/mol. What is the equilibrium constant at 25 °C for the formation of this complex?

A) 1
B) -1
C) 10¹⁰
D) 10^-10
E) cannot be determined

Question 39

The conversion of glucose-6-phosphate to glucose-1-phosphate has a ΔG°′ of 8.4 kJ/mol. What can be said about the value of K_eq?

A) K_eq > 1
B) K_eq = 1
C) K_eq < 1
D) cannot be determined

Question 40

ATP can donate ____ and ____ to lower-energy molecules of metabolism.

A) phosphates, energy
B) reactants, products
C) phosphates, water
D) energy, ΔG
E) ΔG, reactants

Question 41

What role do coupled processes play in biochemical reactions?​